[SILVY968]

<img src="/forum/images/smilies/968/sad.gif" class="smilie" alt="" />

Just found out how much down force the horizontal wing gets at freeway speed.

The pressure cracked the plex at all of the mounting points.

The next design will be made from acrylite, which should be stronger. The horizontal piece will be a frame with the mesh netting over it, or some other design that will stop enough air from flowing back toward the driver from between the seats, yet not offer so much resistance that it stresses the vertical wing mounting points.

Any suggestions are welcome

Partial Post: Please Login or Register to read the full post.

[flash]

bummer - such is life in "parts development land" though - welcome to the club - we're getting jackets made next week



i'm wondering just how fast you were going - i know it's a lot of downforce, exponentially increased with speed, and i know we talked about how effective that piece is, but WOW

Partial Post: Please Login or Register to read the full post.

[SILVY968]

Surprised the crap out of me on the freeway at 65-70 MPH.

A splitering sound behind your ear is very disconcerting!

The down force was may more that I though, but with the horizontal ribs attached to the vertical panel all of the stress was transferred up to the mounting points. also the horizontal panel runs the full size of the rear area from the brace to the toneau cover edge. The 3/16th material was too rigid and did not flex enough. The trick is to either perforate the horizontal wing, redesign the vertical panel to extend down to block the airflow from coming back into the cockpit from between the seats or couple the stress load down to the floor/seat pan.

Back to the drawing board.

Partial Post: Please Login or Register to read the full post.

[flash]

lol - what size jacket do you wear?

Partial Post: Please Login or Register to read the full post.

[SILVY968]

manly medium. What is so funny?

I'll bet you have way more broken prototypes than I do!

By the way it's 80 up here in Seattle, I don't need a jacket.



Any design ideas? I am seriously thinking about a vertical only piece that drops to the floor.

Partial Post: Please Login or Register to read the full post.

[flash]

roflmao - yup - that's for sure



i'd keep in mind the idea of removing and storing in the trunk when thinking about the screen



on that note, if you just gave it some room around it for air to flow a bit, you'd probably not break it



also, put the reinforcing pieces underneath, and change to something that is more vertical (i.e. a .5 x 1 piece on its edge)

Partial Post: Please Login or Register to read the full post.

[smshirk]

[quote name='flash' date='May 17 2006, 11:25 PM']roflmao - yup - that's for sure



i'd keep in mind the idea of removing and storing in the trunk when thinking about the screen



on that note, if you just gave it some room around it for air to flow a bit, you'd probably not break it



also, put the reinforcing pieces underneath, and change to something that is more vertical (i.e. a .5 x 1 piece on its edge)

[right][post="21200"]<{POST_SNAPBACK}>[/post][/right][/quote]





Is there anyone who sells similar bar and wind block for a 968 as the attached Miata upgrade?

Partial Post: Please Login or Register to read the full post.

[flash]

not that i know of



i was asked about that when i was designing mine - i deliberately didn't go that direction because it would never pass pca or scca race spec, regardless of what i did - the specs and requirements are pretty specific, and preclude double hoop bars like that, because of the lack of the required diagonal crossbrace

Partial Post: Please Login or Register to read the full post.

[smshirk]

[quote name='flash' date='Jun 4 2006, 11:18 PM']not that i know of



i was asked about that when i was designing mine - i deliberately didn't go that direction because it would never pass pca or scca race spec, regardless of what i did - the specs and requirements are pretty specific, and preclude double hoop bars like that, because of the lack of the required diagonal crossbrace

[right][post="22320"]<{POST_SNAPBACK}>[/post][/right][/quote]





Was your design a one time deal, or is it availabe somewhere? I think I did see it several months ago, but didn't save the link. I had no idea about the required cross brace. I don't intend to spec race the Miata, but I may not get the added rigidity I was counting on for the SC addition.

Partial Post: Please Login or Register to read the full post.

[flash]

lol, long thread here about it - we did a run, and are planning another run - been tough to nail down the powder coater on a commitment - once i have that, we can do another run - that will probably be the last one for a long time



you can get the roll bar design parameters from any sanctioning body



as for stiffness, it is provided by how it mounts, and triangulation - drilling through sheetmetal to mount gives less structural rigidity than mounting to the frame - every unsupported curve is a weak spot, etc



look closely at any unit before purchasing, and decide what you want out of it - units that give you the "look", usually don't give you the stiffness, and almost never pass inspection - also, do the broomstick test - no real point in a hoop unit if it doesn't pass that - may as well go with in-cabin stuff at that point



in a miata, most of the work you will need to do is in the engine bay and rear suspension, though a roll bar type unit will help the rest of the chassis connect - contact brainstorm - those guys are miata nuts

Partial Post: Please Login or Register to read the full post.

[smshirk]

[quote name='flash' date='Jun 5 2006, 09:40 AM']

lol, long thread here about it - we did a run, and are planning another run - been tough to nail down the powder coater on a commitment - once i have that, we can do another run - that will probably be the last one for a long time



you can get the roll bar design parameters from any sanctioning body



as for stiffness, it is provided by how it mounts, and triangulation - drilling through sheetmetal to mount gives less structural rigidity than mounting to the frame - every unsupported curve is a weak spot, etc



look closely at any unit before purchasing, and decide what you want out of it - units that give you the "look", usually don't give you the stiffness, and almost never pass inspection - also, do the broomstick test - no real point in a hoop unit if it doesn't pass that - may as well go with in-cabin stuff at that point



in a miata, most of the work you will need to do is in the engine bay and rear suspension, though a roll bar type unit will help the rest of the chassis connect - contact brainstorm - those guys are miata nuts

[right][post="22336"]<{POST_SNAPBACK}>[/post][/right]



I am reallly more interested in mods for the 968 than the Miata. I intend to make the Miata a bit more enjoyable to drive over the next few years, but I'm in no hurry. My wife just can't part with it or I would have sold it long ago. I just had it painted, upgraded the wheels and brakes, waiting on Koni's to arrive. I also added the frenzy bar and windscreen in the picture. It works surprisingly well for the cost.



If you are doing another run with the 968 roll bar, or any of your designs for that matter, I would be interested in getting in on the run. The only exception to that at this point is the SC you are contemplating. Although more power would be nice, the 968 is really sufficient for my purposes. I would like to make it more comfortable to drive and improve the looks/ergonomics. I have spent the last two years getting it up to a highly reliable state with most normal maintenance items now replaced. Next on my list are seats, interior refinemnent, suspension improvements, and some cosmetic work on the front bumper and side body molding.



My 996 is in the shop now getting an aero kit installed. If the guy does a good job, then I will have him do the 968 work. Believe it or not, the paint on the 968 has held up better than the 996. It has retained more of its lustre and not picked up the swirl disease nearly as bad. I can't wait to see the aero kit though. He called and said it was finsished but he wasn't happy with it, so I will have to wait another day or two. I hated to do it, but I also had him paint the hood, which was looking bad for a 2000 model.



I was so tempted to sell both P cars and buy a Cayman, I decided to save myself 10s of thousands of dollars and fix up all my current cars. It is more fun i the long run.

[/quote

Partial Post: Please Login or Register to read the full post.